<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>观察者模式</title>
</head>
<body>
    <script>
        // 发布者-目标
        class Dep {
            constructor () {
                // 记录所有的订阅者
                this.subs = []
            }
            // 添加订阅者
            addSub (sub) {
                if (sub && sub.update) {
                    this.subs.push(sub)
                }
            }
            // 发布通知
            notify () {
                this.subs.forEach(sub => {
                    sub.update()
                })
            }
        }

        // 订阅者-观察者
        class Watcher {
            update () {
                console.log('update')
            }
        }

        // 测试
        let dep = new Dep()
        let watcher = new Watcher()

        dep.addSub(watcher)

        dep.notify()
    </script>
</body>
</html>